In the recent years, with the advancement of speeding up of the machines and energy conservation, a toner having excellent low-temperature fixing ability is required. In view of the above, as a resin binder for use in a toner, a polycondensation resin in which an aliphatic polyhydric alcohol is used is proposed, in place of a conventionally used polycondensation resin obtainable from an aromatic polyhydric alcohol.
Patent Publication 1 discloses a toner for electrostatic image development, in which as a resin binder a polyester resin obtainable by reacting an alcohol component containing 1,3-propanediol and a specified other polyhydric alcohol as essential constituents, and a polybasic acid component is used, the toner having excellent fixing ability and offset resistance, showing stable charging behavior even when subjected to continuous printing, and having excellent durability so that an excellent high-quality image is obtained.
Patent Publication 2 discloses a polyester resin for a toner, in which a polyester resin obtainable from a polyol component containing 30 to 100% by mol of an aliphatic diol having 2 to 6 carbon atoms, at least a part of the aliphatic diol being 1,2-propylene glycol, is used, wherein a tetrahydrofuran-soluble component has a number-average molecular weight of from 1,000 to 9,500, for the purpose of providing a toner having excellent balance between low-temperature fixing ability and pulverizability, and excellent gloss after fusing.
For example, Patent Publication 3 discloses a toner for electrostatic image development wherein the polyester contains a high-softening point polyester having a softening point of from 120° to 160° C., and a low-softening point polyester having a softening point of from 75° to 120° C., each obtained by polycondensing an alcohol component consisting essentially of an aliphatic alcohol, and a carboxylic acid component, wherein a difference in the softening points between the high-softening point polyester and the low-softening point polyester is 10° C. or more.
Patent Publication 4 discloses a method for producing a resin binder having excellent triboelectric charges and environmental stability of the image quality, favorable pulverizability and transparency, and being fixable at low temperatures, characterized by previously mixing (a) raw material monomer mixtures of two polymerization system each having independent reaction paths in a single reaction vessel, (b) a compound capable of reacting with the raw materials of both the two polymerization systems, and (c) a tricarboxylic or higher polycarboxylic acid or a derivative thereof, and concurrently carrying out the two polymerization reactions in the same reaction vessel.
In addition, Patent Publication 5 discloses a resin binder for a toner having excellent low-temperature fixing ability, environmental stability, and blocking resistance, the resin binder for a toner containing crystalline polyester and amorphous polyester resins, wherein the crystalline polyester is obtainable by polycondensing an alcohol component containing 70% by mol or more of an aliphatic diol having 2 to 8 carbon atoms, and a carboxylic acid component containing 70% by mol or more of an aromatic dicarboxylic acid compound.
As resin binders for a toner, styrene-acrylic resins, polyesters, epoxy resins and the like have been used, and polycondensation resins such as polyesters are beginning to be widely used because of their excellent low-temperature fixing ability. Patent Publication 6 makes various studies on catalyst usable in the production of a polyester.
Patent Publications 7 and 8 disclose the techniques of adding as a charge control agent a charge control resin (CCR) having excellent triboelectric property.
Patent Publication 9 discloses a toner for electrophotography containing toner particles and at least two kinds of external additives having specified average particle sizes, for the purpose of simultaneous improving transfer efficiency while maintaining high resolution and optical density, and stabilizing fluidity of the toner.
Conventionally, a styrene-acrylic resin or a polyester is known as a resin binder for a toner, and a toner containing a polyester is widely used because of its excellent durability and fixing ability. As the toner as described above, Patent Publication 10 discloses a polyester containing, as a carboxylic acid component, an alkylsuccinic acid and/or alkenylsuccinic acid, having 10 or more carbon atoms, especially from the viewpoint of fixing ability, and a toner obtained by a melt-kneading pulverization method using the polyester as a resin binder. In addition, Patent Publication 11 discloses a toner for electrophotography, containing a resin binder containing a composite resin having a polycondensation resin unit and an addition polymerization resin unit, the toner being obtained by melt-pulverization method, wherein the polycondensation resin unit has a constituting unit derived from a carboxylic acid component containing at least two kinds of alkylsuccinic acid, of which alkyl group is branched and has 9 to 14 carbon atoms.
On the other hand, in the recent years, with the pursuit of formation of high quality images, the development of a toner having a small particle size, the toner having excellent fixing ability is desired. However, in a case where a toner having a small particle size, the toner containing a resin binder containing a polyester as a main component, is produced by a melt-kneading and pulverization method, it is difficult to control the pulverization. In view of the above, for example, Patent Publication 12 discloses a method for producing a toner according to an emulsification-aggregation method, which is a wet production method, using a resin binder having a carboxyl group.
Patent Publication 13 discloses a polyester having excellent hydrolytic resistance usable in the production of a toner including the step of forming particles from raw material components containing a resin binder containing at least a polyester in an aqueous medium or a solution, the polyester being obtainable by polycondensing an alcohol component and a carboxylic acid component containing at least one member selected from alkylsuccinic acids and alkenylsuccinic acids, and a polyester for use in a toner for electrophotography having excellent storage property and fixing ability, containing the above polyester.
Patent Publication 14 discloses, as an objective of providing a toner for electrophotography having excellent storage property and durability, a toner for electrophotography obtainable by a method including the step of forming particles from raw materials containing a resin binder and a polyolefin wax and/or a paraffin wax, wherein the resin binder contains a resin obtainable from at least raw material monomers for a polycondensation resin and raw material monomers for an addition polymerization resin.    Patent Publication 1: JP-A-2002-169331    Patent Publication 2: JP-A-2006-154686    Patent Publication 3: JP-A-2002-287427    Patent Publication 4: JP-A-Hei-7-98517    Patent Publication 5: JP-A-2005-300867    Patent Publication 6: JP-A-2002-148867    Patent Publication 7: JP-A-Hei-9-62035    Patent Publication 8: JP-A-2007-47607    Patent Publication 9: JP-A-Hei-6-332235    Patent Publication 10: JP-A-2007-163682    Patent Publication 11: JP-A-2008-224961    Patent Publication 12: JP-A-2004-198598    Patent Publication 13: JP-A-2007-248582    Patent Publication 14: JP-A-2007-206540